I've never personally dealt with fin rot but the conservative treatment is Aquarium salt. Don't use it for longer than ten days, though... Many medications are pretty harsh on them so I prefer to try salt before anything else.

I believe with fin rot you are looking for fin regrowth and the black edges to disappear... I think they turn white at the edges when they are healing? When the fin rot signs go away, then just warm, clean water and possibly stress coat will help with the healing process.

I used AQ salt and it worked for me = 1tsp/gallon with 100% water changes daily. Extra stress coat helps too, and as always warm, clean water! You should be able to see new fin growth, but the general rule is to use AQ salt for 10 days.